1. Field of the Invention
The present invention relates to internal ureteral stents.
2. Description of Related Art
Internal ureteral stents are generally used to assist movement of urine along a patient's ureter and into the patient's bladder in patients with ureteral obstructions or injury, or to protect the integrity of the ureter in a variety of surgical manipulations. Ureteral stents may be used to treat or avoid ureteral obstructions, such as ureteral stones or ureteral tumors, which disrupt the flow of urine from the kidneys to the bladder. Serious obstructions may cause urine to back up into the kidneys, threatening renal function.
Generally, ureteral stents are formed from a flexible material having sufficient resiliency to allow it to be straightened for insertion into the body passageway, while having sufficient memory to return to its predetermined retentive shape when in situ. Ureteral stents are positioned in the ureter by various procedures that are known to those of skill in the art including antegrade (percutaneous) placement, retrograde (cystoscopic) placement through the urethra, as well as by open ureterotomy or surgical placement in the ureter under direct visual placement. Ureteral stent positioning may be accomplished by several methods known to those of skill in the art.
Typical ureteral stents are tubular in shape, terminating in two opposing ends: a kidney (upper) end and a bladder (lower) end. The ends may be coiled to prevent the upward or downward migration of the stent. The kidney coil is designed to retain the stent within the renal pelvis of the kidney and to prevent stent migration down the ureter. The bladder coil sits in the bladder and is designed to prevent stent migration upwards toward the kidney. The bladder coil may also be used to aid in retrieval and removal of the stent. Currently, the upper and lower coiled ends of ureteral stents are offset by 180° and lie in substantially the same plane. Based on the anatomy of the kidney and bladder, this usually places the coiled, bladder end right on the trigone or just above it.
Ureteral stents, particularly the portion positioned in the ureter near the bladder and inside the bladder, may produce adverse effects including blood in the urine, a continual urge to urinate, and flank pain accompanying reflux of urine up the stent (e.g. when voiding) as pressure within the bladder is transmitted to the kidney. In short, stents may cause or contribute to significant patient discomfort and serious medical problems.